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DWR Weather and Climate News for 9/17/09

Posted by: Maven on September 18, 2009 at 7:59 am

From DWR meteorologist Elissa Lynn, it’s Weather & Climate News:

“Wacky weather? Well, its been an interesting few weeks, with hurricane remnants, Sierra monsoonal storms, and the occasional late-summer, breezy low pressure system! Computer models flip flop a bit in spring and fall, and there’s a mixed prediction for about 7-10 days out. In general, though, we’re dry and warm, looking ahead to the seasons’ change.

Drought conditions remain in place. WY 2007-08 was the first of these three dry years, resulting in 63 percent of average annual precipitation across the state. WY 2008-09 resulted in 72 percent of average annual precipitation. By the end of August, 2009 (most recent data), statewide precipitation stands at 78 percent of average. So the third dry year is about in the can. We look to this winter for ‘wetter and better.’ This season, on its own, was nearly average over the Northern Sierra. The 8-Station index is at 93% of average. That didn’t translate to average runoff, though, as the numbers below will show. Reasons for that include a dry January, and late season storms that didn’t contribute a great deal to snowpack.

In spite of the three dry years, those heavy spring rains lead to decent, non-abysmal reservoir conditions. Statewide reservoir storage at the end of August, 2009 was 79 percent of average for the date, with individual key reservoirs lower than the average. 79 percent isn’t great, but it coulda been much worse. For statewide conditions, by region, or river basin please see:

http://cdec.water.ca.gov/cgi-progs/reservoirs/STORSUM

For daily current conditions, using easily readable bar graphs, please go here:
http://cdec.water.ca.gov/cgi-progs/products/rescond.pdf

For a nice, new product that shows past year and comparative traces for individual reservoir storage, go here:
http://cdec.water.ca.gov/reservoir_map.html …”

Quick breakdown shows the following for end of August reservoir storage:
% Ave / % Cap
NORTH COAST 61 / 43
SAN FRANCISCO BAY 102 / 62
CENTRAL COAST 63 / 37
SOUTH COAST 87 / 60
SACRAMENTO 76 / 51
SAN JOAQUIN 92 / 54
TULARE LAKE 67 / 25
NORTH LAHONTAN 44 / 24
SOUTH LAHONTAN 104 / 76
NORTH COAST 53 / 26
COLORADO RIVER 69 / 55

Runoff numbers: Water Year 2005-06 was the most recent wet  year in California, with 172 percent of average statewide runoff.  Water Year 2006-07 ended with 53 percent of average statewide runoff. The Sacramento River region was classified as  “Dry,” that year, the second driest of five classification levels, and the San Joaquin River region was classified as  Critical,” the driest level. Water Year 2007-08 ended with 60 percent of average statewide runoff, and both the Sacramento and San Joaquin River regions classified as “Critical.”
Water Year 2008-09 is projected to end with 68 percent of average statewide runoff, and both river regions being classified as “Dry.”

These 3 years will likely be near the top-10 driest 3 year stretches on record, the last 100-110 years or so. Will get that  ranking out mid to late October.

Here’s a fun thing. For the major drought report that came out at the end of June, I took a look at the top 10 storm periods of the past season, including intensity, and storm track. We had a decent storm very early on, in October, then a whopper late in May. The info isn’t easily written in text, as it’s a nice graphic with storm amounts over the Northern Sierra shown by colored arrows. Take a look, and special thanks to Cordi McDaniel and Maury Roos of DWR:

http://www.water.ca.gov/drought/docs/Drought_report_30june2009_web.pdf
(see page 4 of the report, page 12 of the pdf)

Additional detailed hydrologic information is available on CDEC:
http://cdec.water.ca.gov/

El Nino….warmer than average equatorial sea surface temperatures over the eastern Pacific Ocean, is still the going trend. Ocean conditions reflect a warm-up that started in April, and now are about 0.5 to 1.5 degrees C above average. They have to stick around a few more months to be an official El Nino, not just the warm conditions that are now in place; it can’t be ‘called,’ till November. But NOAA’s climate prediction center says, that ‘based on current observations and dynamical model forecasts, El Nino is expected to strengthen and last through Northern Hemisphere winter 2009-10′.

The Department of Water Resources doesn’t forecast ocean trends. But here’s a look at what’s transpired over the last eight strong El Nino time periods, based on dates given by CPC:

http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml

Strong El Nino corresponding water year, and state hydrologic data (8 Station is the Northern Sierra):

8 Station, April 1 Water Year, % of Average data

Year/Precipitation/Snowpack/Statewide Runoff

1957-58 / 141 / 171 / 162
1965-66 / 72 / 83 / 77
1972-73 / 103 / 148 / 103
1982-83 / 177 / 227 / 207
1986-87 / 57 / 59 / 52
1987-88 / 69 / 29 / 52
1991-92 / 72 / 60 / 47
1997-98 / 164 / 158 / 169

So, El Nino can bring either wetter or drier than normal conditions. A detailed analysis would include better timing correlation between the onset and the water year dates. These are just raw, general figures for your interest. The impact of a strong El Nino is better defined in Southern California than for the Sierra or statewide numbers shown above. For good So-Cal El Nino information, see the Los Angeles National Weather  Service page devoted to the topic:

http://www.wrh.noaa.gov/lox/main.php?suite=safety&page=el_nino

Flood season is nearly upon us. Although the semi-official start to the season is mid-October, we just have to see how quickly things get started. Major reservoirs upstate still clearly have some room to fill.
Flash flooding, or debris flows are possible any year, and may be the newsmakers this season. With the combination of a potential El Nino, which, when strong, can lead to heavier precip along the coast, rather than necessarily heavy snowpack or a mainstem deluge, along with a substantial burn of the San Gabriel Mountains, concern is heightened.

Pre-Season flood briefings for water managers, flood emergency responders, and flood preparedness and response coordinators are being held at the following locations:

September 21 1:30-4:00pm; Ventura Co. Watershed Protection District Office September 22 9:00-11:30am; Santa Barbara Co. SB Public Health Dept September 23 9:00-11:30am; San Bernardino Co. S Bernardino City Hall September 24 9:00-11:30am; Caltrans, San Diego October 14 1:30-4:00pm; Shasta Co OES, Redding October 15 9:00-11:30am; Whiteaker Hall, Yuba City October 22 9:00-11:30am; Sacramento Sac OES

October 27 1:30-4:00pm; San Joaquin Co OES, Stockton October 29 Isleton; TBD November 17 Eureka; TB

For agencies interested in more information, please contact the State-Federal Flood Operations Center at 916-574-2619.

Although not as frequent, the newsletter remains, for now, a viable entity. Hopefully as the rainy season gets underway, there will be opportunities to publish more often. An end to furloughs would help! But weekly per-storm detailed letters are not likely this winter.”

September 18, 2009 · Filed Under Drought, Weather & Snowpack

Comments

One Response to “DWR Weather and Climate News for 9/17/09”

  1. Kevin Wattier on September 18th, 2009 5:26 pm

    Thanks for posting this. It has great info.on El Nino versus precip in California. What this shows is, there is absolutely no relationship between strong El Nino conditions and precipitation in California. Four of eight strong El Nino’s were wetter than normal, and four of eight were drier than normal. 1986-87, 1987-88, and 1991-92 were strong El Nino’s. These were three of the six years of our last great drought.

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